We have developed a modified version of the original microcytotoxicity test, which is rapid and totally objective (counting of cells being done electronically with an image analyzer), and antibody binding assay based on the use of radioiodinated protein A, and a modified radioimmunoprecipitation test. We have used these assays with mouse sarcomas (as to rats and human patients. Using the in vivo rat bladder tumor model, we are investigating the suppressor and/or blocking factors in transplanted and primary tumors. We have been able to adopt the Milstein hybridoma technique to raise monoclonal antibodies to mouse sarcomas, and recently also to antigens associated with mouse bladder carcinomas and a human melanoma line. We have also been able to establish several lines of typical mouse bladder carcinoma cells, which grow well in culture. This has made it possible to vastly expand our planned experiments, trying to find the specificity, and the chemical nature, of antigens associated with bladder carcinomas in mice and man. Monoclonal antibodies have been raised to such antigens (using heteroimmunization procedures in the experiments with human material), and these antibodies used to make immunoadsorbents for purifying the tumor antigens.